Fix age key generation to convert pubkey to string

Change-Id: I8eb1c7ec0c865f02e2830c8fea2b3307a517972e
Signed-off-by: garciadeblas <gerardo.garciadeblas@telefonica.com>
diff --git a/osm_nbi/base_topic.py b/osm_nbi/base_topic.py
index 252a72a..35514a5 100644
--- a/osm_nbi/base_topic.py
+++ b/osm_nbi/base_topic.py
@@ -1018,7 +1018,7 @@
     def _generate_age_key(self):
         ident = x25519.Identity.generate()
         # gets the public key
-        pubkey = ident.to_public()
+        pubkey = str(ident.to_public())
         # gets the private key
         privkey = str(ident)
         # return both public and private key